In recent years, reduction of electric power consumption, high speed printing, variations of a recording medium, image quality improvement and reduction of environmental load have been required in a printing field in which image formation is carried out according to electro-photography. The toner employed for image formation has been required to have increased fixing strength and a low temperature fixing ability such that a toner image can be fixed at a temperature lower than a conventional fixing temperature, and to realize reduction of carbon dioxide evolution during the manufacture.
The toner usually comprises a resin having a binding ability (a toner binder). As the toner binders, there are known a styrene-acryl resin, a polyester resin, and a hybrid resin such as a polyester resin with an acryl resin grafted.
In response to the demand as described above, a technology is known which improves the toner binders, thereby improving low temperature fixing ability of the toner (refer to Japanese Patent O.P.I. Publication Nos. 2007-279714, 2008-287229 and 2010-15159).
Generally, the styrene-acryl resin has advantage in that it can be synthesized at a low temperature as compared with the polyester resin. Further, the styrene-acryl resin has advantage in that a toner manufacturing process from polymerization of the monomer to toner particle formation can be carried out in an aqueous medium, which is advantageous in toner manufacture.
However, the styrene-acryl resin has disadvantage in that when a paper with a basis weight of from 200 to 350 g/m2 is employed as a recording medium, it is poor in toner adhesion at a folded portion of the recoding medium, as compared with a toner comprising a polyester resin.
As is described above, the manufacture of a toner with both excellent productivity and excellent low temperature fixing ability has been difficult.